Non-Keynesian effects of a fiscal policy tightening are explained in two major ways. According to one group of economists, such effects occur only if public finances are on the verge of a crisis. These effects are caused by a credible, i.e. appropriately strong reduction of the deficit. They stem from the impact of the fiscal policy on the level of uncertainty. According to another group of economists, non-Keynesian effects of a fiscal policy tightening occur not so much due to the scale of the primary imbalance in the public finances, but to the way of balance regaining. Deficit reduction, regardless of its scale necessary to regain balance in public finances and regardless of the public debt volume, may be accompanied by an accelerated output growth if the deficit is reduced not by increasing taxes but by expenditure cuts, especially those for general government sector wages and social transfers. Non-Keynesian effects result from supply effects, e.g. improved competitiveness of domestic companies in international markets. Blanchard's Model (1990), providing the first explanation for non-Keynesian effects, is supplemented in the article with three types of public expenditure, i.e. neutral to the choices made by households, and expenditure that increases and alleviates negative effects of disorders caused by the taxation system on the output level. Such a modification was introduced in order to compare the impact of fiscal consolidation (performed through increasing taxes or through reducing specific categories of public spending) on the total demand. It was shown that even if we assume, as was the case in the model, that the main source of non-Keynesian effects of a fiscal policy tightening is its impact on the level of uncertainty, the influence of fiscal consolidation on the total demand still depends on the way in which the consolidation was implemented. Reductions in public spending never bring about worse results than increased taxes.